Dimensionally stable closed cell rigid polyisocyanate based foam prepared from a froth foaming mixture

ABSTRACT

There is now provided a closed cell rigid polyisocyanate based foam blown with a C 1  -C 4  hydrofluorocarbon and formic acid as blowing agents, which possesses a uniform density gradient varying by not more than 10 percent. There is also now provided a polyol composition and a froth foaming mixture having good flow by employing a polyol and formic acid in the presence of a C 1  -C 4  hydrofluorocarbon having a boiling point of 300K or less as co-blowing agents. The polyol composition advantageously has an average OH number of less than 400 and an average functionality of greater than 4, which when reacted with the isocyanate in the presence of a C 1  -C 4  hydrofluorocarbon, yields a rigid closed cell polyisocyanate based dimensionally stable foam having a fine cell structure.

This is a divisional, of application Ser. No. 08/367,032 filed Dec. 29, 1994, now U.S. Pat. No. 5,762,822.

FIELD OF THE INVENTION

The present invention pertains to polyol compositions and dimensionally stable closed cell rigid polyisocyanate based foams made thereby, and more particularly to foaming reaction mixtures which froth at a dispensing head and which have excellent flow characteristics, employing as a blowing agents a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, preferably 1,1,1,2-tetrafluroethane, and formic acid or salts thereof.

BACKGROUND OF THE INVENTION

Various hydrofluorocarbons have been investigated in the industry as blowing agents for polyisocyanate based foams due to their low or nonexistent ozone depletion potentials. U.S. Pat. No. 4,997,706 discloses the use of closed cell rigid polyurethane foams blown with a C₁ -C₄ hydrofluorocarbon along with a blowing agent precursor such as water in amounts effective to lower the thermal conductivity of the foam relative to a similar foam made in the absence of the hydrofluorocarbon. Such rigid thermal insulation foams are generally poured or sprayed into a cavity or mold to make residential or commercial refrigeration cabinets, entry doors, or other applications where insulation is advantageous. The cavities into which the foaming mixture is poured or sprayed are often large and/or contain complex shapes which make it difficult for the foaming mixture to uniformly penetrate. In the case of a large cavity, the foam front begins to gel making it increasingly difficult for the mixture to cover the whole cavity and foam to a uniform density. The advantageous thermal insulation properties of the foam are defeated if gaps are left in the cavity where the foaming mixture could not penetrate, if bubbles form as a result of the foam shrinking due to poor dimensional stability, or if the density gradient is non-uniform which in turn leads to gaps or poor dimensional stability.

The flow characteristics of a foaming mixture becomes particularly critical when one employs a blowing agent which instantly volatilizes at atmospheric pressure and temperature, causing the foam to froth at the dispensing head. An example of such a blowing agent is 1,1,1,2-tetrafluoroethane (R-134a). A frothed foam has the consistency much like a shaving cream, which renders it difficult to evenly flow throughout a cavity.

When manufacturing a rigid closed cell polyisocyanate based foam in a cavity or pour in place application, the average hydroxyl number of the polyols are generally over 400 to increase the crosslinking density, provide structural strength, and prevent foam shrinkage. The higher the average hydroxyl number, however, the more isocyanate one must consume at an equivalent isocyanate index and the faster the ingredients react. It would be desirable to increase the formulation latitude and processing window by decreasing the average hydroxyl number of the polyols, with the attendant advantage of reducing the amount of isocyanate consume and slowing the reaction down to afford improved flow characteristics. Adding high levels of blow catalyst in an effort to improve flow actually impedes the flow and impairs foam properties because the high levels of catalyst too rapidly promote the formation of urethane foam matrix. Merely lowering the average hydroxyl number, however, typically results in sacrificing dimensional stability.

It would also be desirable to reduce the amount of hydrofluorocarbon, such as R-134(a), employed due to its cost, while retaining the same density of a foam blown with the original amount of the hydrofluorocarbon. Merely adding more water, however, tends to gel the foam quicker, which reduces the flow characteristics of the foaming mixture, degrades the dimensional stability of the foam, and causes the foam to have a coarse cell structure.

SUMMARY OF THE INVENTION

There is now provided a closed cell rigid polyisocyanate based foam having a closed cell content of at least 85% blown with a combination of a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, preferably 1,1,1,2-tetrafluroethane, and formic acid or salts of formic acid. The foam advantageously has a uniform density gradient varying by not more than 10 percent and a fine cell structure. A foam with a good density gradient indicates that the foaming mixture flowed well.

There is also provided a polyol composition comprising a) compounds having at least two isocyanate reactive hydrogens, b) formic acid or salts of formic acid, and c) a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, preferably 1,1,1,2-tetrafluoroethane. In one embodiment, the a) compounds are hydroxyl terminated polyols having an average OH number of less than 400 and an average functionality of greater than 4, which when reacted with the isocyanate in the presence of a C₁ -C₄ hydrofluorocarbon, yields a mixture which has good flow and a rigid closed cell polyisocyanate based dimensionally stable foam.

Also described is a method of making a closed cell rigid polyisocyanate based foam having a closed cell content of at least 85%, comprising ejecting through a dispensing head an isocyanate stream and a polyol composition stream at a weight ratio of 0.9:1 to 1.3:1, respectively, in the presence of a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, wherein the polyol composition stream comprises a) compounds having at least two isocyanate reactive hydrogens; and b) formic acid or salts of formic acid.

The formulations described herein have the advantage of reducing the amount of C₁ -C₄ hydrofluorocarbon needed without sacrificing the dimensional stability of the foam or the flow characteristics of the foaming mixture at densities equivalent to the higher levels of hydrofluorocarbon which would otherwise have to be employed.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms of art are to be understood according to the accompanying definitions:

A "uniform density gradient" means that the overall density of the foam does not vary by more than 10 percent from the core density taken from the same foam. The percentage variation is measured according to the following formula: ##EQU1## where O.D. is the overall density and C.D. is the core density The panel is packed to 10 percent beyond the theoretical value needed to completely fill the mold volume, and the free rise density of the foaming mixture employed is 1.9 pcf or less. The test is run by using a foam panel measured and taken from a 2'×4'×2" mold from which the overall density is measured, and a core sample measuring 3"×3"×1" taken from any point along the length of the panel and at about the center of its width. Test panels which do not have the above measurements across the entire respective surfaces are not used for determining the density gradient and would in any case indicate extremely poor flow characteristics. At no point should the density gradient anywhere on the foam panel vary by more than 10 percent.

A "polyol composition" contains at least formic acid as a blowing agent and a compounds having at least two isocyanate reactive hydrogens.

A "compound having at least two isocyanate active hydrogens" has a number average molecular weight of greater than 400.

A "froth foaming mixture" is a combination of a polyol composition stream and an organic polyisocyanate stream in the presence of a C₁ -C₄ hydrofluorocarbon which may be mixed with the polyol composition, the polyisocyanate stream, or both; where the C₁ -C₄ hydrofluorocarbon sufficiently and spontaneously vaporizes when the two combined streams are exposed to atmospheric pressure upon discharge from the dispensing head to produce a froth. It is to be understood that not all of the C₁ -C₄ hydrofluorocarbon needs to vaporize instantaneously from the two stream mixture when discharged, but at least an amount sufficient to produce a froth upon discharge and prior to entry into a cavity or onto a substrate.

Turning to the polyol composition, there is provided an a) compound having at least two isocyanate active hydrogens and b) formic acid or salts of formic acid. In one embodiment, the C₁ -C₄ hydrofluorocarbon is added to the a) and b) compounds to form a polyol composition. In another embodiment, the hydrofluorocarbon can be added only to the isocyanate compound, or it can be added to both the isocyanate and as part of the polyol composition.

The compounds having at least two isocyanate active hydrogens have an average hydroxyl number ranging from 150 to 800 mgKOH/g of compound having at least two isocyanate active hydrogens. In a preferred embodiment, however, the average hydroxyl number is less than 400 and the average functionality is greater than 4.0., and more preferably, the average hydroxyl number is 350 or less and the average functionality is 4.5 or more. These average hydroxyl numbers are unusual in that the typical rigid polyurethane foam is made with polyols whose average hydroxyl number exceeds 400 so as to provide the rigidity and structural strength necessary to make a dimensionally stable foam. However, in the present invention, a dimensionally stable foam is provided with a polyol combination that has a low average hydroxyl number. Further, by providing a low average hydroxyl number, the flow characteristics of the froth foaming mixture are enhanced, and less isocyanate is consumed at any given isocyanate index. It is to be understood that in the preferred embodiment, compounds having at least two isocyanate active hydrogens whose hydroxyl numbers exceed 400 can be employed so long as the average hydroxyl number of all such compounds is less than 400. The a) compounds are also preferably hydroxyl terminated compounds such as polyoxyalkylene polyether polyols, polyester polyols, or mixtures thereof.

Examples of compounds having at least two isocyanate active hydrogens include polythioether polyols, polyester amides and polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, amine terminated polyoxyalkylene polyethers, and preferably, polyester polyols, polyoxyalkylene polyether polyols, and graft dispersion polyols. In addition, mixtures of at least two of the aforesaid polyols can be used as long as the combination has an average hydroxyl number in the aforesaid range.

The term "polyester polyol" as used in this specification and claims includes any minor amounts of unreacted polyol remaining after the preparation of the polyester polyol and/or unesterified polyol (e.g., glycol) added after the preparation of the polyester polyol. The polyester polyol can include up to about 40 weight percent free glycol.

Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbons, and multivalent alcohols, preferably diols, with 2 to 12 carbons, preferably 2 to 6 carbons. Examples of dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives may also be used such as dicarboxylic acid mono- or di- esters of alcohols with 1 to 4 carbons, or dicarboxylic acid anhydrides. Dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid in quantity ratios of 20-35:35-50:20-32 parts by weight are preferred, especially adipic acid. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerine and trimethylolpropanes, tripropylene glycol, tetraethylene glycol, tetrapropylene glycol, tetramethylene glycol, 1,4-cyclohexane-dimethanol, ethanediol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures of at least two of these diols are preferred, especially mixtures of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Furthermore, polyester polyols of lactones, e.g., ε-caprolactone or hydroxycarboxylic acids, e.g., ω-hydroxycaproic acid, may also be used.

The polyester polyols can be produced by polycondensation of organic polycarboxylic acids, e.g., aromatic or preferably aliphatic polycarboxylic acids and/or derivatives thereof and multivalent alcohols in the absence of catalysts or preferably in the presence of esterification catalysts, preferably in an atmosphere of inert gases, e.g., nitrogen, carbon dioxide, helium, argon, etc., in the melt at temperatures of 150° to 250° C., preferably 180° to 220° C., optionally under reduced pressure, up to the desired acid value which is preferably less than 10, especially less than 2. In a preferred embodiment, the esterification mixture is subjected to polycondensation at the temperatures mentioned above up to an acid value of 80 to 30, preferably 40 to 30, under normal pressure, and then under a pressure of less than 500 mbar, preferably 50 to 150 mbar. The reaction can be carried out as a batch process or continuously. When present, excess glycol can be distilled from the reaction mixture during and/or after the reaction, such as in the preparation of low free glycol-containing polyester polyols usable in the present invention. Examples of suitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts. However, the polycondensation may also be preformed in liquid phase in the presence of diluents and/or chlorobenzene for aziotropic distillation of the water of condensation.

To produce the polyester polyols, the organic polycarboxylic acids and/or derivatives thereof and multivalent alcohols are preferably polycondensed in a mole ratio of 1:1-1.8, more preferably 1:1.05-1.2.

After transesterification or esterification, the reaction product can be reacted with an alkylene oxide to form a polyester polyol mixture. This reaction desirably is catalyzed. The temperature of this process should be from about 80° to 170° C., and the pressure should generally range from about 1 to 40 atmospheres.

While the aromatic polyester polyols can be prepared from substantially pure reactant materials, more complex ingredients are advantageously used, such as the side stream, waste or scrap residues from the manufacture of phthalic acid, terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, and the like.

Other residues are DMT process residues, which are waste or scrap residues from the manufacture of dimethyl terephthalate (DMT). The term "DMT process residue" refers to the purged residue which is obtained during the manufacture of DMT in which p-xylene is converted through oxidation and esterification with methanol to the desired product in a reaction mixture along with a complex mixture of byproducts. The desired DMT and the volatile methyl p-toluate byproduct are removed from the reaction mixture by distillation leaving a residue. The DMT and methyl p-toluate are separated, the DMT is recovered and methyl p-toluate is recycled for oxidation. The residue which remains can be directly purged from the process or a portion of the residue can be recycled for oxidation and the remainder diverted from the process or, if desired, the residue can be processed further as, for example, by distillation, heat treatment and/or methanolysis to recover useful constituents which might otherwise be lost, prior to purging the residue from the system. The residue which is finally purged from the process, either with or without additional processing, is herein called DMT process residue.

Polyoxyalkylene polyether polyols, which can be obtained by known methods, are particularly preferred for use as the compounds having at least two isocyanate active hydrogens. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides such as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate, or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one initiator molecule containing 2 to 8, preferably 3 to 8, reactive hydrogens or by cationic polymerization with Lewis acids such as antimony pentachloride, boron trifluoride etherate, etc., or bleaching earth as catalysts from one or more alkylene oxides with 2 to 4 carbons in the alkylene radical. Any suitable alkylene oxide may be used such as 1,3-propylene oxide, 1,2-and 2,3-butylene oxide, amylene oxides, styrene oxide, and preferably ethylene oxide and 1,2-propylene oxide and mixtures of these oxides. The polyalkylene polyether polyols may be prepared from other starting materials such as tetrahydrofuran and alkylene oxide-tetrahydrofuran mixtures; epihalohydrins such as epichlorohydrin; as well as aralkylene oxides such as styrene oxide. The polyalkylene polyether polyols may have either primary or secondary hydroxyl groups, preferably secondary hydroxyl groups from the addition of propylene oxide onto an initiator because these groups are slower to react.

Included among the polyether polyols are polyoxyethylene glycol, polyoxypropylene glycol,polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4-tetramethylene and polyoxyethylene glycols, and copolymer glycols prepared from blends or sequential addition of two or more alkylene oxides. The polyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U.S. Pat. No. 1,922,459. Polyethers which are preferred include the alkylene oxide addition products of polyhydric alcohols such as ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone, resorcinol glycerol, glycerine, 1,1,1-trimethylol-propane, 1,1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol, α-methyl glucoside, sucrose, and sorbitol. Also included within the term "polyhydric alcohol" are compounds derived from phenol such as 2,2-bis(4-hydroxyphenyl)-propane, commonly known as Bisphenol A.

Particularly preferred in the polyol composition is at least one polyol which is initiated with a compound having at least two primary or secondary amine groups, a polyhydric alcohol having 4 or more hydroxyl groups, such as sucrose, or a mixture of initiators employing a polyhydric alcohol having at least 4 hydroxyl groups and compounds having at least two primary or secondary amine groups.

Suitable organic amine initiators which may be condensed with alkylene oxides include aromatic amines such as aniline, N-alkylphenylene-diamines, 2,4'-, 2,2'-, and 4,4'-methylenedianiline, 2,6- or 2,4-toluenediamine, vicinal toluenediamines, o-chloro-aniline, p-aminoaniline, 1,5-diaminonaphthalene, methylene dianiline, the various condensation products of aniline and formaldehyde, and the isomeric diaminotoluenes; and aliphatic amines such as mono-, di-, and trialkanolamines, ethylene diamine, propylene diamine, diethylenetriamine, methylamine, triisopropanolamine, 1,3-diaminopropane, 1,3-diaminobutane, and 1,4-diaminobutane. Preferable amines include monoethanolamine, vicinal toluenediamines, ethylenediamines, and propylenediamine.

Suitable polyhydric polythioethers which may be condensed with alkylene oxides include the condensation product of thiodiglycol or the reaction product of a dicarboxylic acid such as is disclosed above for the preparation of the hydroxyl-containing polyesters with any other suitable thioether glycol.

The hydroxyl-containing polyester may also be a polyester amide such as is obtained by including some amine or amino alcohol in the reactants for the preparation of the polyesters. Thus, polyester amides may be obtained by condensing an amino alcohol such as ethanolamine with the polycarboxylic acids set forth above or they may be made using the same components that make up the hydroxyl-containing polyester with only a portion of the components being a diamine such as ethylene diamine.

Polyhydroxyl-containing phosphorus compounds which may be used include those compounds disclosed in U.S. Pat. No. 3,639,542. Preferred polyhydroxyl-containing phosphorus compounds are prepared from alkylene oxides and acids of phosphorus having a P₂ O₅ equivalency of from about 72 percent to about 95 percent.

Suitable polyacetals which may be condensed with alkylene oxides include the reaction product of formaldehyde or other suitable aldehyde with a dihydric alcohol or an alkylene oxide such as those disclosed above.

Suitable aliphatic thiols which may be condensed with alkylene oxides include alkanethiols containing at least two --SH groups such as 1,2-ethanedithiol, 1,2-propanedithiol, 1,2-propanedithiol, and 1,6-hexanedithiol; alkene thiols such as 2-butene-1,4-dithiol; and alkyne thiols such as 3-hexyne-1,6-dithiol.

Also suitable as the polyol are polymer modified polyols, in particular, the so-called graft polyols. Graft polyols are well known to the art and are prepared by the in situ polymerization of one or more vinyl monomers, preferably acrylonitrile and styrene, in the presence of a polyether or polyester polyol, particularly polyols containing a minor amount of natural or induced unsaturation. Methods of preparing such graft polyols may be found in columns 1-5 and in the Examples of U.S. Pat. No. 3,652,639; in columns 1-6 and the Examples of U.S. Pat. No. 3,823,201; particularly in columns 2-8 and the Examples of U. S. Pat. No. 4,690,956; and in U.S. Pat. No. 4,524,157; all of which patents are herein incorporated by reference.

Non-graft polymer modified polyols are also useful, for example, those prepared by the reaction of a polyisocyanate with an alkanolamine in the presence of a polyol as taught by U.S. Pat. Nos. 4,293,470; 4,296,213; and 4,374,209; dispersions of polyisocyanurates containing pendant urea groups as taught by U.S. Pat. No. 4,386,167; and polyisocyanurate dispersions also containing biuret linkages as taught by U.S. Pat. 4,359,541. Other polymer modified polyols may be prepared by the in situ size reduction of polymers until the particle size is less than 20 μm, preferably less than 10 μm.

The closed cell rigid polyisocyanate based foam of the invention is blown with at least two blowing agents: b) formic acid or salts thereof, and a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less. The blowing agents which can be used may be divided into the chemically active blowing agents which chemically react with the isocyanate or with other formulation ingredients to release a gas for foaming, and the physically active blowing agents which are gaseous at the exotherm foaming temperatures or less without the necessity for chemically reacting with the foam ingredients to provide a blowing gas. Included with the meaning of physically active blowing agents are those gases which are thermally unstable and decompose at elevated temperatures.

The b) formic acid, upon contact with an isocyanate group, reacts to initially liberate carbon monoxide and further decomposes to form an amine with a release of carbon dioxide. Aside from its zero ozone depletion potential, a further advantage of using formic acid is that two moles of gas are released for every mole of formic acid present, whereas a water-isocyanate reaction results in the release of only one mole of gas per mole of water. In both water-isocyanate and formic acid-isocyanate reactions, the isocyanate is consumed and one must add a proportionate excess of isocyanate to compensate for the loss. However, since formic acid is a more efficient blowing agent than water, the moles of formic acid necessary to produce the same moles of gas as a water-isocyanate reaction is greatly reduced, thereby reducing the amount of excess isocyanate and leading to a substantial economic advantage. The amount of isocyanate needed to make an equivalent density foam is 5 to 30 weight percent less when one employs formic acid or mixtures thereof over an all water-blown formulation.

A further advantage of using formic acid in the polyol composition of the invention is its contribution of the improved flowability of the reaction mixture. Without being bound to a theory, it is believed that the formic acid-isocyanate reaction proceeds in the following two-step reaction: ##STR1##

It is believed that liberation of carbon monoxide and subsequently carbon dioxide in the above reaction proceeds at a slower rate than the release of carbon dioxide in a water-isocyanate reaction for two reasons: a) the anhydride is more stable than the carbamic acid formed in a water-isocyanate reaction and, therefore, requires more thermal energy to decompose, and b) the above reaction is a two step reaction rather than a one step reaction present in a water-isocyanate reaction. Lower exotherms, especially at the onset of the reaction, are significant because the energy driving the reaction between the isocyanate and polyols is lowered, thereby enhancing flow and avoiding a rapid gel front buildup. In an all water blown system, the reaction between the isocyanate and water proceeds quickly and raises the exotherm earlier, thereby promoting a quicker urethane matrix formation as evidenced by the faster gel time. By contrast, the polyurethane matrix formation from the cream to the gel time in the formic acid containing polyol composition of the invention does not proceed as quickly due to the lower exotherm at an equivalent point in time. The lower exotherm and longer gel times are another factor in the invention which allow the reactive mixture to flow further without encountering the fast setting urethane matrix in the hotter and higher water containing systems.

The b) formic acidiformate ions in the polyol composition may be supplied by addition of formic acid or a mixture of formic acid and soluble salts of formic acid. Suitable salts of formic acid include the amine or ammonium salts of weakly base mono, di, or trialkylamines, including hydrazine, triethylamine, dimethylbenzylamine, and triethylenediamine. Many of these tertiary amine salts of formic acid act in a dual capacity as a source of formate ions for gas production and as a catalyst for the reaction between isocyanate and compounds having isocyanate reactive hydrogens. It is preferred that the formate ions present in the polyol composition are supplied by the addition of an excess of formate ion/formic acid equivalents to the number of catalytically active tertiary amine equivalents and, more preferred, also to the number of other tertiary amine equivalents including fully substituted amine initiated polyoxyalkylene polyether polyols which can react in situ with formic acid. Suitable examples include an equivalent ratio of formate ion/formic acid equivalents to catalytically active tertiary amine sites of at least 1.1:1, and the same would be a suitable example for the ratio of formate ion/formic acid equivalents to all tertiary amine centers present in the polyol composition.

Suitable concentrations of formic acid are any commercially available, ranging from about 90% pure to 100% pure, with the remainder being water and in some cases acetic acid depending upon the source.

The polyol composition contains formic acid or a mixture of formic acid and salts of formic acid, and one may add additional chemically reactive blowing agents such as water, tertiary alcohols, other 2 to 20 carbon atom mono or poly carboxylic acids having molecular weights from 46 to 300 and their amine or ammonium salts. Preferably, water is used as the additional blowing agent in the polyol composition. Further, water is usually present in commercially available formic acid. Water reacts with the organic isocyanate to liberate CO₂ gas which is the actual blowing agent. However, since water consumes isocyanate groups, an equivalent molar excess of isocyanate must be used to make up for the consumed isocyanates.

If organic carboxylic acids are additionally used, suitable examples would include aliphatic mon- and polycarboxylic acids, e.g. dicarboxylic acids. However, other organic mono- and polycarboxylic acids are also suitable. The organic carboxylic acids may, if desired, also contain substituents which are inert under the reaction conditions of the polyisocyanate polyaddition or are reactive with isocyanate, and/or may contain olefinically unsaturated groups. Specific examples of chemically inert substituents are halogen atoms, such as fluorine and/or chlorine, and alkyl, e.g. methyl or ethyl. The substituted organic carboxylic acids could contain at least one further group which is reactive toward isocyanates, e.g. a mercapto group, a primary and/or secondary amino group, or preferably a primary and/or secondary hydroxyl group.

Suitable carboxylic acids are thus substituted or unsubstituted monocarboxylic acids, e.g. formic acid, acetic acid, propionic acid, 2-chloropropionic acid, 3-chloropropionic acid, 2,2-dichlorpropionic acid, hexanoic acid, 2-ethyl-hexanoic acid, cyclohexanecarboxylic acid, dodecanoic acid, palmitic acid, stearic acid, oleic acid, 3-mercapto-propionic acid, glycoli acid, 3-hydroxypropionic acid, lactic acid, ricinoleic acid, 2-aminopropionic acid, benzoic acid, 4-methylbenzoic acid, salicylic acid and anthranilic acid, and unsubstituted or substituted polycarboxylic acids, preferably dicarboxylic acids, e.g. oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, glutaric acid, adipic acid, sebacic acid, dodecanedioic acid, tartaric acid, phthalic acid, isophthalic acid and citric acid.

Combinations of any of the aforementioned chemically active blowing agents may be employed, such as formic acid, or salts of formic acid, and water.

As a physically active blowing agent, at least a C₁ -C₄ hydrofluorocarbon blowing agent having a boiling point of 300K or less, preferably 273K or less, is employed in the invention.

Suitable C₁ -C₄ hydrofluorocarbons include difluoromethane (HFC-32); 1,1,1,2-tetrafluoroethane (HFC-134a); 1,1,2,2-tetrafluoroethane (HFC-134); 1,1-difluoroethane (HFC-152a); 1,2-difluoroethane (HFC-142), trifluoromethane; heptafluoropropane (R-227a); hexafluoropropane (R-136); 1,1,1-trifluoroethane; 1,1,2-trifluoroethane; fluoroethane (R-161); 1,1,1,2,2-pentafluoropropane; pentafluoropropylene (R-2125a); 1,1,1,3-tetrafluoropropane; tetrafluoropropylene (R-2134a); difluoropropylene (R-2152b); 1,1,2,3,3-pentafluoropropane; and 1,1,1,3,3-pentafluoro-n-butane.

In a preferred embodiment, the physically active blowing agent is at least 1,1,1,2-tetrafluoroethane (R-134a), and more preferably R-134a is the sole physically active blowing agent used because of its wide availability, its zero ozone depletion potential, and its excellent frothing characteristics. R-134a has a boiling point of 247K (-26° C. at 760 mm/Hg) and readily vaporizes at atmospheric pressure to froth a foaming mixture as it exits a dispensing head. R-134a, and other C₁ -C₄ hydrofluorocarbons, may be added to the polyol composition at the dispensing head as a separate stream; blended into the polyol composition tank immediately prior to dispensing; pre-blended into the polyol composition, stored and shipped in pressurized containers to a foam manufacturer, added to the isocyanates in the isocyanate stream, or added to both the polyol composition and the isocyanate stream. To make a formulated polyol composition by any of these methods, R-134a, or any of the other C₁ -C₄ hydrofluorocarbons, is liquified if necessary under pressure, metered to the polyol composition, and optionally but preferably blended until a homogenous solution is formed. Tanks containing the polyol composition are pressurized at 200-300 psig, and depending on the type of dispensing method employed as discussed further below, may also be pressurized with an inert gas such as nitrogen.

The amount of C₁ -C₄ hydrofluorocarbons employed, including R-134a, will depend upon the desired density and the limits of its solubility in a particular polyol composition. To reduce costs, it is always advantageous to keep the amount of hydrofluorocarbon to a minimum within the desired density range.

In the polyol composition of the invention, amounts of formic acid/salts are generally used are generally from 2.0 weight percent to 7.0 weight percent, with 3.5 to 5.5 weight percent being an preferred optimal range, based on the weight of the polyol composition. Amounts of R-134a added to the polyol composition range are from 3.0 to 10 parts by weight, preferably from 5 pbw to 9 pbw, based on the weight of the froth foaming composition which includes the isocyanate and polyol composition. With regard to R-134(a), at amounts of less than 3.0 weight percent, such as about 2 weight percent based on the weight of the froth foaming composition, the foaming mixture does not froth. Therefore, to form a froth, at least 3.0 weight percent of R-134a should be used, based on the weight of the foaming composition. At these amounts of R-134a and formic acid, we have been able to produce rigid closed cell polyisocyanate based foams having low free rise densities ranging from 1.5 pcf to 1.9 pcf and low overall molded densities ranging from 2.0 pcf to 2.5 pcf, more preferably from 2.1 pcf to 2.3 pcf.

Other physically active blowing agents which may be used in combination with the b) formic acid or salts thereof and the C₁ -C₄ hydrofluorocarbon are those which boil at the exotherm foaming temperature or less, preferably at 50° C. or less. The most preferred physically active blowing agents are those which have an ozone depletion potential of 0.05 or less. Examples of physically active blowing agents are the volatile non-halogenated hydrocarbons having two to seven carbon atoms such as alkanes, alkenes, cycloalkanes having up to 6 carbon atoms, dialkyl ethers, cycloalkylene ethers and ketones; hydrochlorofluorocarbons (HCFCs); hydrofluorocarbons (HFCs) having more than 4 carbon atoms or which boil at more than 300K; perfluorinated hydrocarbons (HFCs); fluorinated ethers (HFCs); and decomposition products.

Examples of volatile non-halogenated hydrocarbons include linear or branched alkanes, e.g. butane, isobutane, 2,3 dimethylbutane, n- and isopentane and technical-grade pentane mixtures, n- and isohexanes, n- and isoheptanes, n- and isooctanes, n- and isononanes, n- and isodecanes, n- and isoundecanes, and n- and isododecanes. Since very good results are achieved with respect to the stability of emulsions, the processing properties of the reaction mixture and the mechanical properties of polyurethane foam products produced when n-pentane, isopentane or n-hexane, or a mixture thereof is used, these alkanes are preferably employed. Furthermore, specific examples of alkenes are 1-pentene, 2-methylbutene, 3-methylbutene, and 1-hexene, of cycloalkanes are cyclobutane, preferably cyclopentane, cyclohexane or mixtures thereof, specific examples of linear or cyclic ethers are dimethyl ether, diethyl ether, methyl ethyl ether, vinyl methyl ether, vinyl ethyl ether, divinyl ether, tetrahydrofuran and furan, and specific examples of ketones are acetone, methyl ethyl ketone and cyclopentanone. Preferentially, cyclopentane, n- and isopentane, n-hexane, and mixtures thereof are employed.

Hydrochlorofluorocarbon blowing agents include 1-chloro-1,2-difluoroethane; 1-chloro-2,2-difluoroethane (142a); 1-chloro-1,1-difluoroethane (142b); 1,1-dichloro-1-fluoroethane (141b); 1-chloro-1,1,2-trifluoroethane; 1-chloro-1,2,2-trifluoroethane; 1,1-dichloro-1,2-difluoroethane; 1-chloro-1,1,2,2-tetrafluoroethane (124a); 1-chloro-1,2,2,2-tetrafluoroethane (124); 1,1-dichloro-1,2,2-trifluoroethane; 1,1-dichloro-2,2,2-trifluoroethane (123); and 1,2-dichloro-1,1,2-trifluoroethane (123a); monochlorodifluoromethane (HCFC-22); 1-chloro-2,2,2-trifluoroethane (HCFC-133a); gem-chlorofluoroethylene (R-1131a); chloroheptafluoropropane (HCFC-217); chlorodifluoroethylene (HCFC-1122); and trans-chlorofluoroethylene (HCFC-1131). The most preferred hydrochlorofluorocarbon blowing agent is 1,1-dichloro-1-fluoroethane (HCFC-141b).

Perfluorocarbons or fluorinated ethers include hexafluorocyclopropane (C-216); octafluorocyclobutane (C-318); perfluorotetrahydrofuran; perfluoroalkyl tetrahydrofurans; perfluorofuran; perfluoro-propane, -butane, -cyclobutane, -pentane, -cyclopentane, and -hexane, -cyclohexane, -heptane, and -octane; perfluorodiethyl ether; perfluorodipropyl ether; and perfluoroethyl propyl ether.

Catalysts may be employed which greatly accelerate the reaction of the compounds containing hydroxyl groups and with the modified or unmodified polyisocyanates. Examples of suitable compounds are cure catalysts which also function to shorten tack time, promote green strength, and prevent foam shrinkage. Suitable cure catalysts are organometallic catalysts, preferably organotin catalysts, although it is possible to employ metals such as lead, titanium, copper, mercury, cobalt, nickel, iron, vanadium, antimony, and manganese. Suitable organometallic catalysts, exemplified here by tin as the metal, are represented by the formula: R_(n) Sn X-R¹ -Y!₂, wherein R is a C₁ -C₈ alkyl or aryl group, R¹ is a C₀ -C₁₈ methylene group optionally substituted or branched with a C₁ -C₄ alkyl group, Y is hydrogen or an hydroxyl group, preferably hydrogen, X is methylene, an --S--, an --SR² COO--, --SOOC--, an --O₃ S--, or an --OOC-- group wherein R² is a C₁ -C₄ alkyl, n is 0 or 2, provided that R¹ is C₀ only when X is a methylene group. Specific examples are tin (II) acetate, tin (II) octanoate, tin (II) ethylhexanoate and tin (II) laurate; and dialkyl (1-8C) tin (IV) salts of organic carboxylic acids having 1-32 carbon atoms, preferably 1-20 carbon atoms, e.g., diethyltin diacetate, dibutyltin diacetate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dihexyltin diacetate, and dioctyltin diacetate. Other suitable organotin catalysts are organotin alkoxides and mono or polyalkyl (1-8C) tin (IV) salts of inorganic compounds such as butyltin trichloride, dimethyl- and diethyl- and dibutyl- and dioctyl- and diphenyl- tin oxide, dibutyltin dibutoxide, di(2-ethylhexyl) tin oxide, dibutyltin dichloride, and dioctyltin dioxide. Preferred, however, are tin catalysts with tin-sulfur bonds which are resistant to hydrolysis, such as dialkyl (1-20C) tin dimercaptides, including dimethyl-, dibutyl-, and dioctyl- tin dimercaptides.

Tertiary amines also promote urethane linkage formation, and include triethylamine, 3-methoxypropyidimethylamine, triethylenediamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl- and N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine or -hexanediamine, N,N,N'-trimethyl isopropyl propylenediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, 2-dimethyaminoethyl-1,3-dimethylaminopropyl ether, N,N-dimorpholinoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1-methyl-4-dimethylaminoethylpiperazine, 1,2-dimethylimidazole, 1-azabicylo 3.3.0!octane and preferably 1,4-diazabicylo 2.2.2!octane, and alkanolamine compounds, such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.

To prepare polyisocyanurate (PIR) and PUR-PIR foams by the process according to the invention, a polyisocyanurate catalyst is employed. Suitable polyisocyanurate catalysts are alkali salts, for example, sodium salts, preferably potassium salts and ammonium salts, of organic carboxylic acids, expediently having from 1 to 8 carbon atoms, preferably 1 or 2 carbon atoms, for example, the salts of formic acid, acetic acid, propionic acid, or octanoic acid, and tris(dialkylaminoethyl)-, tris(dimethylamninopropyl)-, tris(dimethylaminobutyl)- and the corresponding tris(diethylaminoalkyl)-s-hexahydrotriazines. However, (trimethyl-2-hydroxypropyl)ammonium formate, (trimethyl-2-hydroxypropyl)ammonium octanoate, potassium acetate, potassium formate and tris(diemthylaminopropyl)-s-hexahydrotriazine are polyisocyanurate catalysts which are generally used. The suitable polyisocyanurate catalyst is usually used in an amount of from 1 to 10 parts by weight, preferably form 1.5 to 8 parts by weight, based on 100 parts by weight of the polyol composition.

The polyol composition may also contain a flame retardant. Examples of suitable phosphate flameproofing agents are tricresyl phosphate, tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate, and tris(2,3-dibromopropyl) phosphate. In addition to these halogen-substituted phosphates, it is also possible to use inorganic or organic flameproofing agents, such as red phosphorus, aluminum oxide hydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate (Exolit®) and calcium sulfate, molybdenum trioxide, ammonium molybdate, ammonium phosphate, pentabromodiphenyloxide, 2,3-dibromopropanol, hexabromocyclododecane, dibromoethyldibromocyclohexane, expandable graphite or cyanuric acid derivatives, e.g., melamine, or mixtures of two or more flameproofing agents, e.g., ammonium polyphosphates and melamine, and, if desired, corn starch, or ammonium polyphosphate, melamine, and expandable graphite and/or, if desired, aromatic polyesters, in order to flameproof the polyisocyanate polyaddition products. In general, from 2 to 40 pbw of said flameproofing agents may be used based on the weight of the polyol composition and isocyanate stream.

The organic polyisocyanates include all essentially known aliphatic, cycloaliphatic, araliphatic and preferably aromatic multivalent isocyanates. Specific examples include: alkylene diisocyanates with 4 to 12 carbons in the alkylene radical such as 1,12-dodecane diisocyanate, 2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, 1,4-tetramethylene diisocyanate and preferably 1,6-hexamethylene diisocyanate; cycloaliphatic dilsocyanates such as 1,3- and 1,4-cyclohexane diisocyanate as well as any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 2,4- and 2,6-hexahydrotoluene diisocyanate as well as the corresponding isomeric mixtures, 4,4'-2,2'-, and 2,4'-dicyclohexylmethane diisocyanate as well as the corresponding isomeric mixtures and preferably aromatic diisocyanates and polyisocyanates such as 2,4- and 2,6-toluene diisocyanate and the corresponding isomeric mixtures 4,4'-, 2,4'-, and 2,2'-diphenylmethane diisocyanate and the corresponding isomeric mixtures, mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanates and polyphenylenepolymethylene polyisocyanates (polymeric MDI), as well as mixtures of polymeric MDI and toluene diisocyanates. Crude polyisocyanates may also be used in the compositions of the present invention, such as crude toluene diisocyanate obtained by the phosgenation of a mixture of toluenediamines or crude diphenylmethane isocyanate obtained by the phosgenation of crude diphenylmethane diamine. The preferred or crude isocyanates are disclosed in U.S. Pat. No. 3,215,652. The organic di- and polyisocyanates can be used individually or in the form of mixtures. The preferred isocyanate is polymeric MDI.

Frequently, so-called modified multivalent isocyanates, i.e., products obtained by the partial chemical reaction of organic diisocyanates and/or polyisocyanates are used. Examples include diisocyanates and/or polyisocyanates containing ester groups, urea groups, biuret groups, allophanate groups, carbodiimide groups, isocyanurate groups, and/or urethane groups. Specific examples include organic, preferably aromatic, polyisocyanates containing urethane groups and having an NCO content of 33.6 to 15 weight percent, preferably 31 to 21 weight percent, based on the total weight, e.g., with low molecular weight diols, triols, dialkylene glycols, trialkylene glycols, or polyoxyalkylene glycols with a molecular weight of up to 1500; modified 4,4'-diphenylmethane diisocyanate or 2,4- and 2,6-toluene diisocyanate, where examples of di- and polyoxyalkylene glycols that may be used individually or as mixtures include diethylene glycol, dipropylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, and polyoxypropylene polyoxyethylene glycols or -triols. Prepolymers containing NCO groups with an NCO content of 25 to 9 weight percent, preferably 21 to 14 weight percent, based on the total weight and produced from the polyester polyols and/or preferably polyether polyols described below; 4,4'-diphenylmethane diisocyanate, mixtures of 2,4'- and 4,4'-diphenylmethane diisocyanate, 2,4,- and/or 2,6-toluene diisocyanates or polymeric MDI are also suitable. Furthermore, liquid polyisocyanates containing carbodiimide groups having an NCO content of 33.6 to 15 weight percent, preferably 31 to 21 weight percent, based on the total weight, have also proven suitable, e.g., based on 4,4'- and 2,4'- and/or 2,2'-diphenylmethane diisocyanate and/or 2,4'- and/or 2,6-toluene diisocyanate. The modified polyisocyanates may optionally be mixed together or mixed with unmodified organic polyisocyanates such as 2,4'- and 4,4'-diphenylmethane diisocyanate, polymeric MDI, 2,4'- and/or 2,6-toluene diisocyanate.

While the isocyanate compound stream may be mixed with the polyol composition stream at a wide range of weight ratios, an advantageous feature of the formulated polyol composition allows one to mix the two streams at a weight ratio of from 0.9:1 to 1.3:1 respectively, preferably at a 1:05 to 1.15:1 weight ratio, and at an isocyanate index ranging from 100 to 130, preferably at 105 to 120, while obtaining a foam having excellent dimensional stability at the low densities mentioned above. Prior polyurethane foam formulations, however, were reacted at an iso/polyol weight ratio of from about 1.5:1 to 2:1 at isocyanate indices of 100 to 130, which required a larger amount of isocyanate to stoichiometrically react with the isocyanate reactive groups at equivalent isocyanate indices. Thus, the formulation of the invention and the method of dispensing allows one to manufacture a dimensionally stable foam using much smaller quantities of isocyanate.

In another feature of the invention, the froth foaming mixture can be dispensed at a constant flow regardless of pressure changes at the outlet of the dispensing head, thus obviating the need for using positive displacement flow control units or for metering the iso stream and polyol stream into the dispensing head at different flow rates. In this embodiment, the froth foaming mixture can be dispensed from a portable foaming apparatus as disclosed in U.S. Pat. Nos. 3,541,023 and 3,769,232, each of which is incorporated herein by reference. While the use of a static mixing device as the dispensing head is particularly preferred, the polyol composition along with the C₁ -C₄ hydrofluorocarbon frothing agent can be employed in low pressure equipment having rotary mechanical mix dispensing heads or on high pressure equipment using impingement mix dispensing heads.

Typically, the portable foaming apparatus is comprised of at least two reactants supply tanks, a static mixer having inlets in communication with the supply tanks and an outlet for expelling the mixed reactants, means for imposing gas pressure to drive the reactants from the supply tanks, through and out of the static mixer, and flow control units for delivering the desired ratio of reactants, from their respective tanks, to the static mixer.

One of the supply tanks contains the organic isocyanate reactant or an organic isocyanate-terminated quasi-prepolymer or prepolymer. If desired, this tank may also contain an additive amount of a non-reactive fire-retardant material which may be used to impart flame retardant properties to the resulting foam. This tank may also contain R-134a and other non-reactive blowing agents in liquid form, but it is preferred to add at least part of the R-134a and other blowing agents to the polyol composition supply tanks. The other polyurethane foam forming reactants may be supplied from one or more additional polyol composition supply tanks. Usually a single second tank is used to supply all these other reactants, i.e., polyol, foaming agent, catalyst, and surfactant, if such is used.

Any means for imposing pressure to drive the reactants from the supply tanks through and out of the static mixer may be used. Typically, a pressurized gaseous inert propellant, such as a nitrogen tank, is used having valved outlets communicating via suitable conduits with the inlets to the supply tanks. The supply tanks are kept under pressure to provide the driving force needed to propel the reactants from the supply tanks and to liquify the R-134a blowing agent in the formulated polyol compositions supply tank(s). The pressure in the supply tanks is generally 200-250 psig.

It is generally necessary, for the proper functioning of the portable foaming apparatus, that the viscosity of the contents of each of the supply tanks be no greater than about 1000 cps at 78° F. and more preferably no more than about 800 cps. This, of course, means that the materials in each tanks may have to be properly selected or formulated, as the case may be, in order to meet this viscosity requirement. The formulated polyol composition according to the invention advantageously has a very low viscosity of 550 cps or less, even lower than 400 cps, rendering the formulation eminently suitable for use in the portable foaming apparatus. The viscosity values mentioned herein are measured at 78° F. and at 80 psig. The viscosity of supply tanks contents are measured under a pressure of 80 psig because of the presence of R-134a or other volatile hydrofluorocarbons in liquid form. The portable foaming apparatus comprises a static mixer which is one containing no moving parts. Any such mixer which serves to adequately blend the reactants may be used. Illustrative of such a mixer is the one disclosed in U.S. Pat. No. 3,286,992.

By employing a portable foaming apparatus, the volume ratio of the isocyanate stream to the formulated polyol composition stream can be held at 1:1±0.1, or as pointed out above, at weight ratio in a preferable range of 1:05 to 1.15:1, thereby reducing the amount of isocyanate required to make a foam at a desired isocyanate index.

The isocyanate stream and the polyol composition stream are propelled by the inert gas under pressure into a dispensing head to form a foamable mixture which is ejected from the dispensing head through a static mixer dispensing head as a froth foaming mixture, which is a partially expanded foaming mixture much akin to the consistency of shaving cream, but which continues to expand on or in the application site to its full molded or free rise volume. The foamable mixture contains the liquid C₁ -C₄ hydrofluorocarbon frothing agent having a boiling point of 300K or less, and preferably a formulated polyol composition is employed so that only two liquid streams enter the dispensing head. Although the foamable mixture exiting the dispensing head, preferably through a static mixer, is in the form of a froth, the froth foaming mixture according to the invention has excellent flow characteristics as demonstrated by the uniform density gradient of the resulting polyisocyanate based rigid closed cell foam.

In a more preferred embodiment, the foams made with the formulated polyol composition have a uniform density gradient which varies by not more than 10 percent, most preferably by not more than 6 percent. The high amount of blow catalyst, the low levels of water as a co-blowing agent, the low viscosity of the formulated polyol composition, and the low average hydroxyl number of the polyols all have a combined effect of producing a froth foaming mixture which flows well and produces a low density foam having excellent dimensional stability.

The polyurethane foams made according to the invention are dimensionally stable, meaning that the percent volume change of a 3"×3"×1" core sample tested according to ASTM D 2126-87 taken from a 10 percent overpacked mold measuring 2'×4'×2" is less than ±5 percent, at -20° F., 158° F., 200° F., 100° F. and 100 percent relative humidity, and 158° F. and 100 percent relative humidity. Preferably, the percent volume change is less than ±4 percent, and more preferably ±3 percent or less.

The polyisocyanate based foams of the invention have a closed cell content of at least 85 percent, preferably 90 percent or more, and most preferably 95 percent or greater. The foams of the invention also are rigid, meaning that they have a high ratio of compressive strength to tensile strength of 0.5:1 or greater and an elongation of 10 percent or less.

Polyurethane foams prepared by the process of the invention have utility in a variety of applications in which the foam is generated on-site from a portable foaming apparatus. This includes the production of foam-core structural and architectural panels and partitions, building and vehicular insulation, marine flotation devices, water heater insulation, refrigeration cabinets and panels, entry doors, picnic coolers, and a variety of molded objects for use in home furnishing.

The following examples are intended to illustrate, but in no way limit, the scope of the present invention. The following examples are provided to illustrate the invention. The foaming apparatus used in these examples was identical to the apparatus disclosed in U.S. Pat. No. 3,769,232 except that it did not include the valved timing assembly embodied in the apparatus of that patent. Thus, the apparatus comprised (a) a first supply tank for supplying the isocyanate reactant, (b) a second supply tank for supplying the other foam forming ingredients, (c) a nitrogen pressure tank having a valved outlet in communication, via a distributing valve, with the inlets to the two supply tanks, (d) a static mixer having one outlet and two inlets communicating with the supply tanks outlets, and (e) adjustable flow control units interposed in the conduits linking the supply tank with the static mixer.

The polyols employed in the working examples are defined as follows:

Polyol A is a propylene oxide/ethylene oxide adduct of a mixture of a vicianl toluene diamine/ethylene diamine amine intiators having a nominal OH# of 300, commercially available from BASF Corporation.

Polyol B is a propylene oxide adduct of a sucrose/amine mixture having a nominal hydroxyl number of 530, commercially available from Olin Corporation.

Polyol C is a propylene oxide adduct of a sucrose/amine mixture having a nominal hydroxyl number of 350, commercially available from Olin Corporation.

Niax L5440 is a silicone surfactant commercially available from Union Carbide.

PCF is Fyrol PCF, a flame retardant, available from Great Lakes Chemical.

DABCO 8154 is a 2-ethyl-hexanoic acid blocked triethylene diamine, commercially available from Air Products.

DABCO DC-2 is a delayed action amine based catalyst available from Air Products.

EXAMPLE 1

The portable foaming apparatus referred to above was employed to prepare a frothed, rigid, molded polyurethane foam using the procedure and ingredients described herein.

The foam forming ingredients were supplied from two cylindrical metal tanks. One supply tank contained the Iso A reactant, namely, polymethylene polyphenylene isocyanate. This material is commercially available under the trademark LUPRANATE® M20S, a product of BASF Corporation. The other supply tank, the total content of which had a viscosity of 410 cps at 77° F. for Sample 1 and 375 cps at 77° F. for sample 2, when measured at 80 psig; contained the following ingredients in Table 1 in the indicated relative proportions as weight percent.

                  TABLE 1     ______________________________________     INGREDIENTS        SAMPLE 1  SAMPLE 2     ______________________________________     Polyol A           44.92     75.94     Polyol B           16.48     17.51     Polyol C           25.00     0.0     PCF                7.00      0.0     L5540              2.0       2.2     DABCO DC-2         0.1       0.0     DABCO 8154         0.0       0.25     FORMIC ACID.sup.1  4.5       4.0     TOTAL              100       100     R-134a     PERCENT IN POLYOL COMP.                        7.0       7.0     ISO A              100       100     R-134a     PERCENT IN ISO A   7.00      7.00     INDEX              110       110     WEIGHT RATIO       100/93    100/93     OF ISO/POLYOL COMP.     ______________________________________      .sup.1 A solution of 94% formic acid in 6% water.

Both of the two supply tanks were placed horizontally on a drum roller and rotated continuously for two hours at an approximate rate of 35 revolutions per minute. After the rotation was stopped, the inlets to the two supply tanks were connected to the nitrogen pressure tank and the pressure was increased to 240 psig. The tanks outlets were connected to the static mixer via separate conduits provided with flow control units. With the flow control units adjusted to deliver to the static mixer equal weight proportions from the first and second supply tanks, the foam forming ingredients were expelled, by means of the nitrogen head pressure, from their respective tanks, through the static mixer, and out into an aluminum mold preheated to 90° F. and having the dimensions 2'×4'×2". The results are reported below in Table 2.

                  TABLE 2     ______________________________________     PROPERTIES        SAMPLE 1   SAMPLE 2     ______________________________________     Density, f.r., 6" Core                       1.4 pcf    1.4 pcf     from 2' × 2' × 2' Box     Density, f.r., #10 Lily cup                       1.5 pcf    1.5 pcf     Gel Time          2'15"      1'50"     Tack Free Time    3'30"      3'00"     Weight Ratio     Iso/Resin         100/93     100/93     Test Panel 2' × 4' × 2"     Overall Density   2.2 pcf    2.25 pcf     Core Density      2.05 pcf   2.10 pcf     % Variance        7 percent  7 percent     Compressive Strength (yield)     Parallel          26         28     Perpendicular     22         21     U.L. 94 HF-1     Average Self-Extinguish                       40 seconds 36 seconds     Average Damage Length                       46 mm      45 mm     % Closed cell, uncorrected                       90         92     % Volume Change, 14 Days     -20° F.    -0.1       0.4     158° F.    -1.1       -1.5     200° F.    -1.0       -1.2     100° F. + 100% R.H.                       -2.2       -1.5     158° F. + 100% R.H.                       -3.4       2.5     ______________________________________ 

What I claim is:
 1. A froth foaming mixture comprising an organic polyisocyanate compound having at least two isocyanate groups, and a polyol composition comprising:a) compounds having at least two isocyanate reactive hydrogens; b) formic acid or salts of formic acid, said further comprising a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less.
 2. The froth foaming mixture of claim 1, wherein said C₁ -C₄ hydrofluorocarbon comprises 1,1,1,2-tetrafluoroethane.
 3. The froth foaming mixture of claim 1, wherein, wherein the polyol composition contains 1,1,1,2-tetrafluoroethane.
 4. The froth foaming mixture of claim 2, wherein the amount of 1,1,1,2-tetrafluoroethane is 4 p.b.w. or more based on 100 p.b.w. of the system.
 5. The froth foaming mixture of claim 1, wherein 80 wt. % or more of said a) compounds comprise polyoxyalkylene polyether polyols.
 6. The froth foaming mixture of claim 5, wherein said polyoxyalkylene polyether polyols are initiated with initiators comprising compounds containing at least two primary or secondary amine groups.
 7. The froth foaming mixture of claim 6, wherein said initiators comprise toluene diamine, a C2-C6 aliphatic polyamine, or mixtures thereof.
 8. The froth foaming mixture of claim 1, wherein the average hydroxyl number of the polyol composition is less than 400 and the average functionality is 4.0 or greater.
 9. The froth foaming mixture of claim 2, wherein compound b) comprises formic acid in an amount ranging from 3.0-7.0 wt. % or more based on the weight of the polyol composition.
 10. The froth foaming mixture of claim 1, wherein said b) compound comprises formic acid.
 11. The froth foaming mixture of claim 2, wherein said system is reacted to form a rigid closed cell polyisocyanate based foam having a closed cell content of at least 85%.
 12. The froth foaming mixture of claim 11, wherein said foam has a uniform density gradient varying by not more than 10 percent.
 13. The froth foaming mixture of claim 11, wherein said foam has a free rise density of 1.5 to 1.9 pcf using 3.0 to 9 p.b.w. of 1,1,1,2-tetrafluoroethane based on the weight of the isocyanate and polyol composition, and 3.5 to 5.0 wt. % of formic acid based on the weight of the polyol composition.
 14. The froth foaming mixture of claim 11, wherein the foam has an overall molded density of from 2.0 to 2.5 p.c.f.
 15. The froth foaming mixture of claim 10, wherein wherein a froth foaming mixture is produced by injecting at a dispensing head said polyol composition and an isocyanate stream comprising said polyisocyanate, in the presence of 1,1,1,2-tetrafluoroethane, at a weight ratio of 0.9:1 to 1.3:1.
 16. The froth foaming mixture of claim 1, wherein said polyol composition is reacted with said polyisocyanate compound at a weight ratio between 1.05:1 and 1.15:1, respectively, and at an isocyanate index of 105 to
 115. 17. A method of making a closed cell rigid polyisocyanate based foam having a closed cell content of at least 85%, comprising ejecting through a dispensing head an isocyanate stream and a polyol composition stream at a weight ratio of 0.9:1 to 1.3:1, respectively, and at an isocyanate index ranging from 100 to 130, in the presence of a C₁ -C₄ hydrofluorocarbon having a boiling point of 300K or less, wherein the polyol composition stream comprises:a) compounds having at least two isocyanate reactive hydrogens; and b) formic acid or salts of formic acid.
 18. The method of claim 17, wherein the C₁ -C₄ hydrofluorocarbon comprises 1,1,1,2,-tetrafluoroethane.
 19. The method of claim 18, wherein the isocyanate stream and the polyol composition stream are propelled to the dispensing head by an inert gas.
 20. The method of claim 18, wherein the isocyanate stream is reacted with the polyol composition stream at an isocyanate index of 105 to 115 and at a weight ratio of 1.05:1 to 1.15:1.
 21. The method of claim 18, wherein the polyol composition stream and the isocyanate stream are ejected by an inert gas under pressure through a static mixer.
 22. The method of claim 18, wherein the average hydroxyl number of the a) compounds having at least two isocyanate active hydrogens is less than 400 and the average functionality of the a) compounds is 4.0 or more. 